Differential effects of chronic stress on Fos- reactivity and phospho-CREB expression in isolated and mixed-gender pair-housed male and female rats

Submitted Chapter 6 104 Chronic stress is thought to be an important factor in the aetiology of depression, whereas social support has stress-reducing properties and a positive influence on the course of a depressive episode. 21 Days of chronic footshock stress was used as a model for affective disorders in rats and group housing of rats could provide a suitable model for social support to study the underlying neurobiological mechanisms. Male and female rats were either individually or socially housed in mixed-gender pairs. Limbic Fos expression and phospho-CREB in the dentate gyrus were used as markers of stress coping. In socially housed males most brain areas analysed showed a stress-induced increased Fos expression, whereas in isolated males stress-induced increases were lower and reached significance only in the PVN, prelimbic and anterior cingulate cortex, and median raphe nucleus. Stress exposure affected Fos-ir only in the SON and MPN of isolated females, whereas socially housed females showed increased Fos-ir in more regions. Phospho-CREB expression in the dentate gyrus was increased after stress in socially but not in individually housed males. In isolated females, pCREB expression was decreased, which could not be prevented by pair-housing. In conclusion: Social housing appeared to increase Fos reactivity to stress, but it augmented DG pCREB expression in males. In females pair-housing with a male only had slight ameliorating effects, but was superior to isolation. Abstract Neurobiology mixed-gender groups